Telmisartan is known from EP 0502314B and has the following chemical structure of formula (I):

Telmisartan is an angiotensin II receptor antagonist, which by virtue of its pharmacological properties is particularly useful in the treatment of hypertension and cardiac insufficiency.
Chinese Patent CN 1344172 discloses the preparation of telmisartan in two steps: namely condensation and hydrolysis.
U.S. Pat. No. 5,591,762 discloses the preparation of telmisartan from its tertiary butyl ester. Hydrolysis is carried out using trifluoro acetic acid in dimethyl formamide at room temperature and maintained for about 12 hours. The crude product obtained is purified over a silica gel column and finally crystallized from acetone.
US 2002/0094997 is a divisional application of U.S. Pat. No. 6,358,986. US 2002/0094997 discloses polymorphs of telmisartan, particularly polymorphic form B, polymorphous mixtures and their preparation. Accordingly, telmisartan Form A is dissolved in a mixture of solvents consisting of water, formic acid and an organic solvent that is miscible therewith; the solution is heated followed by distillation and telmisartan containing Form A and Form B is precipitated from the mixture by addition of a base. The disclosure further refers to advantages of the polymorphic Form B mixture, for example it is easily filterable and has a low tendency to electrostatic charging. The disclosure still further refers to the fact that Form A, which is obtained according to the basic patent, is difficult to filter, is characterized by a very long drying time and exhibits a strong tendency to electrostatic charging. The two telmisartan polymorphs of Form A and B as characterised by US 2002/0094997 differ considerably in their melting point: Form B melts at 183° C. (determined by DSC), Form A at 269° C. (determined by DSC). The polymorphs A and B also differ in their IR spectrum. Pure polymorph A has a characteristic band at 815 cm−1 in the IR spectrum. In polymorph B, this oscillation is shifted to 830 cm−1.
In all the prior art processes, telmisartan is prepared in two or three steps, which is time consuming, product is lost during intermediate isolation, and as such there is a resulting low yield of the final product. It is also suggested in the prior art that the use of dimethyl formamide and alkali metal carbonates as solvent resulted in dimer formation, which also contributed to low yield.